… Suppose Hume has impressions of what are in fact eighteenth- century European humans. These impressions can give rise to an idea applicable to and only to eighteenth-century European humans. But they could also give rise to an idea applicable to and only to humans of any time and culture, and also to an idea applicable to and only to persons (i.e. any rational beings, including for example Martians)…

… But if the concept of causation is a concept of regular succession, it is plausible to suppose that it is meaningless even to speculate about single causes, causes which caused effects even though no similar objects causes similar effects…

… claim that since only the conditioned could be an object of possible experience, we can have no knowledge of the ‘unconditioned’… various attempts to acquire knowledge of the unconditioned land us in irresoluble conflicts…

… It was only in 1803 that the first version of an atomic theory of chemistry was proposed by Dalton which gave –by the criteria I expounded – a very probable explanation of the details of observed data (such as the fixed ratios by weight in which substances combined to form new substances). Before Dalton theories about the unobservable were simply unevidenced speculations. Since Dalton, scientists have produced evidence making probable detailed theories not merely about things too small, but about things too big, too old, and too strange to be observed. Kant had great respect for the physical sciences; if he had known of their subsequent history, he might have acknowledged great scope for human reason to acquire probably true beliefs about matters far beyond the observable…